I always find it interesting when people work with the relationship between Luna and Celestia as two loving sisters. Past and present in the canon. It elaborates further on their past what the show didn't, your art tells just a little more stroy and much more to how much they both lost over time.
I thought at first that they flying and those rocks were mountains, the picnic blanket fields. I was wondering "Why is everyone saying how cut this is when it looks like Tia is about to drop poor Luna in the ocean from a real height?" Silly me.